Secondary electron discharge device



Feb. 7, 1939. A. .1. w. M; VAN OVERBEEK ,1

SECONDARY ELECTRON DISCHARGE DEVICE Filed Feb. 15, 1938 -.l fll hl l bhl l INVENTORY AYDRIANUS J.W. M. VAN OVERBEEK Patented Feb. 7, 1939UNITED STATES SECONDARY ELECTRON DISCHARGE DEVICE Adrianus J. W. M. vanOverbeek. Eindhoven,

Netherlands,

assignor to N. V. Philips Gloeilampeniabrleken, Eindhoven, NetherlandsApplication February 15, 1938, Serial No. 190,531 I In the NetherlandsFebruary 6 Claims. (Cl, 250-174) This invention relates to electrondischarge tubes having a secondary emission electrode provided on atleast part of its surface with a substance, such as one of the metals oroxides of the group of alkali or alkaline earth metals, which upon beingstruck by a primary electron stream readily emits secondary electrons.

In discharge tubes of this type the electrodes have been somountedthat'the primary elctrons 10 from the cathode pass through one ormore grids, and then through a grid-like anode to impinge upon asecondary emission electrode located near and behind the' grid-likeanode. The secondary electrons are collected by the grid-like anode, andmay oscillate through and around it to some extent, which isdisadvantageous for short-wave uses. Furthermore, all the electrodes arein the discharge path of the primary electrons. To improve theproperties, particularly the internal re'- 1 20 sistance, of suchdischarge tubes, it has been proposed to construct the tube so that thesecondary electrons issuing from the secondary emission electrode arecollected by an anode mounted outside the discharge path of the primaryelectrons. In tubes thus constructed it has been found that in somecases the secondary electrons are not fully and completely drawn awayfrom the vicinity of the secondary emission electrode. The principalobject of the invention is tovprovide a tube 01 the secondary emissionelectrode type in which the secondary electrons are promptly removedfrom the vicinity of the secondary electron emitter without oscillatingabout an anode, and which is well adapted for short-wave uses. Accordingto the present invention, an electron discharge tube is constructed withan electrode system including a secondary emission electrode and acollector electrode comprising a plate-shaped output anode outside ofand alongside the path or the primary electrons and a grid-likeelectrode or anode extension mounted immediately in front of thesecondary emission electrode and connected tothe platethrough thegrid-like anode extension to the secondary emission electrode and thesecondary electrons which are liberated are rapidly and completely drawnaway from the secondary emission 0 electrode principally to theplate-shaped anode of the collector electrode. The advantages of thesecondary electron emission type of tube are retained, while nodifliculty is experienced from electrons oscillating to and fro aroundthe grid- 5 like anode extension, a feature of particular imof thebeams.

6 shaped output anode. The primary electrons pass portance in the use ofthis type of tube for shortwavepurposes.

According to one particular embodiment of the present invention thesecondary emission electrode is so arranged that any material projectedfrom the primary cathode cannot reach the secondary emission electrode.To this end the primary electrons are constrained to follow curved pathsfrom the primary cathode through the grid-like extension conductivelyconnected to the plate anode mounted to one side of the paths of theprimary electrons, and thus reach the secondary emission electrode,which extends across and is normal to the paths of the primary electronsat a point out of the straight line trajectories of particles thrown offfrom the cathode.

The invention will be explained more fully with reference to theaccompanying drawing, which represents diagrammatically one embodimentof the invention in an electron discharge tube with the electrodesarranged according to the present invention.

The tube shown .in the drawing comprises the usual evacuated envelopeenclosing a conventional indirectly heated rectilinear cathode Iconsisting of a tubular cathode sleeve coated with barium and strontiumoxides, said cathode in turn being surrounded by a coaxial control grid2 and a coaxial screen grid 3,-each of the conventional helical typewith two side rods or supports parallel to said cathode. The side rodsof the grids act to some extent as beam forming electrodes whichconcentrate the primary electron discharge from-the cathode I into twofairly well defined electron beams proceeding from the. cathode indiametrically opposite directions. These beams follow curved paths, as"indicated by the arrows 4, which indicate the path of one The primaryelectrons proceeding from the cathode are led over the curved paths toan emitter anode Shaving a surface coated with a substance, such ascaesium oxide or caesium, which readily emits secondary electrons, sothat the emitter anode has a high coefficient of secondary electronemission.

The emitter anode 5 preferably has a fiat surface treated with asubstance, such as casein oxide, so that it has a high coeflicient .ofsecondary electron emission and on which the primary electron dischargeimpinges. The secondary electrons emitted by the bombarded surface ofthe emitter 5 greatly exceed in number the primary electrons which fallon the emitter. The cmitteranode 5 may, as indicated in the drawing, bemade of sheet metal and in the general venient where, as in the tubeshown in the drawing, all of the discharge from 'the cathode is broughtto the emitter anode. The flat secondary 1 electron emitting surfaces ofthe emitter anode 5 are set edgewise to the cathode and the planes ofthese surfaces are transverse to the direction of the electron dischargeas it leaves the cathode, so that the beams must follow curved andsubstantially semi-circular paths in order to reach the secondaryelectron emitting surfaces of the emitter anode. a

The output current of the tube is secured from a collector electrodecomprising a grid-like anode extension 6 mounted in front of andparallel to the fiat surface of the emitter anode 5 and constituting anextension of an output anode I mounted outside the path of the electrondischarge to the emitter anode. The output anode I is preferably animperforate sheet of metal and is substantially parallel to and to oneside of the path followed by the primary electron discharge from thecathode to the emitter anode. As indicated by the dotted lines, theprimary \electron stream passes through the grid-like extension 6,impinges on the surface of. the emitter anode 5, thus producing a greatnumber of secondary electrons, which are rapidly and completelywithdrawn from the vicinity of the emitter anode and also from thepathof the primary electrons by the positive collector electrode. As

- ondary electrons.

a result of this construction, the trons which pass through thegrid-like anode extension 6 do not oscillate about or through the anodeextension, but are quickly drawn away tothe output anode 1. Due tofreedom from oscillations of the secondary electrons the tube isparticularly suitable for short-wave work. p

The discharge from the cathode is constrained by an acceleratingelectrode 8, which is more or less semi-cylindrical in form andpartially encloses the cathode,-to follow the curved and substantiallysemi-circular paths indicat in the figure by the arrows 4. The fieldproduced by the accelerating electrode 8 causes the discharge from thecathode to fiow in afairly"well defined beam alongside but not touchingthe output anode 1 and through the grid-like anode extension to impingeupon the emitter anode 5 with sufficient velocity to cause copiousemission of sec- Contamination of the secondary electron emit- I tingsurfaces of. the emitter anode 5 by particles thrown off by the cathodeis very unlikely for the reason that particles mionic cathode travel instraight lines and the trajectories of practically all of theseparticles will be such that the particles will miss theemitting surfacesof the emitter anode. To insure that none of the particles thrown offfrom the cathode will reach the emitter anode surfaces a shield 9 may beinterposed between the inner edge of the emitter anode and the cathode.This shield is preferably a sheet of metal set transversely of themedian plane of the cathode and emitter anode, and of such dimensionsthat a straight line cannot be drawn from any point on the surface ofthe cathode to any point on the secondary electhrown off from a ther-'straight lines toward the emitting surfaces of the emitter anode. Theshield may to advantage be connected to the cathode, so that it is atzero potentialand thus actsas an electrostatic shield between thecathode and the emitter anode.

. As illustrated in the drawing, the tube may be connected to a sourceof potential such as a battery In with the negative terminal connectedto the control grid 2 and the positive terminal connected through a loadcircuit II to the collector electrode 1. The discharge may be modulatedby an input circuit I 2 connected to vary the potential of the controlgrid.

I claim: v 1. An electron discharge device comprising an emitter anodehaving a high coeflicient of secondary electron emission, means forproducing a modulated stream of primary electrons to said emitteranodejand'a collector electrode comprising an output anode mountedadjacent said emitter anode and outside of the path of said modulatedprimary electron stream and a gridlike extension of said output anodemounted in front of said emitter anode and athwart the path of saidprimary electron stream to said emitter adjacent said emitter anode andoutside the path of said electron stream and having a gridlike anodeextension connected to said output anode and extending across the pathof said electron stream to said emitter anode, and a shield interposedbetweerrsaid cathode and said emitter anode in position to preventimpingement upon said emitter anode of particles ejected from saidcathode.

3. An electron'discharge device comprising a thermionic cathode,beam-forming electrodes for concentrating the discharge from saidcathode into an electron beam, a plate emitter anode having a highcoefficient of secondary electron emission and mounted edgewise to saidcathode with a flat surface in a plane transverse to the axis of theelectron beam at said'cathode, a curved ac- .celerating electrode withits concave surface facing said cathode and extending from the vicinityof said cathode toward said emitter to constrain said electron beam tofollow a curved path to said surface of said emitter, a collectorelectrode comprising an output anode outside and substantially parallelto the path .of said electron beam adjacent said emitter and a grid-likeextension projecting across the path of said beam and in front of saidemitter.

4. An.electron discharge device comprising a thermionic cathode, anemitter anode having a high coeflicient of secondary electron emission,a collector electrode comprising an output anode adjacent said emitteranode and outside the path of discharge from said cathode to saidemitter and having a grid-like extension across the path of saiddischarge adjacent said emitter, and a solid shield mounted between saidcathode and said emitter and extending across any straight line betweenany point of said emitter surface and any point of said cathode.

5. An electron discharge device comprising a thermionic cathode, emitteranode having a flat surface substantially in a plane extending--radially of said cathode, a collector electrode comprising a solidoutput anode positioned outside the path of discharge from said cathodeto said emitter anode and inclined to said emitting anode surface, saidoutput anode having a grid-like anode extension in front of and parallelto said emitter surface, and a shield interposed between said cathodeand said emitter anode and'constituting a solid physical barrier toparticles which move along a straight line from any point on saidcathode-to any point on said emitter surface.

6. An electron discharge device comprising a rectilinear cathode, a gridsurrounding said cathode and having a pair of side rods parallel to saidcathode, an emitter anode having two flat surfaces inclined to eachother and intersecting at an acute angle with the line of intersectionof the planes of saidsurfaces in alignment with said grid side rods andsaid cathode, a semi-cylindrical accelerating electrode facing saidemitter 'and partially surrounding'said cathode to cause the electrondischarge from said cathode to said emitter to follow curved paths toboth surfaces- ADRIANUS J. W. M. VAN OVERBEEK.

